Peptide and protein sequences can be inserted into the coat proteins of filamentous bacteriophages, enabling these foreign sequences to be displayed on the surfaces of the virus particles. This technology has the potential to open up vast new areas of structural biology, since it is possible to design and prepare phages that display a chosen peptide sequence at or near the N-terminus of the major coat protein. It is also possible to randomize the sequences of the inserted peptide, providing a powerful tool for the generation of libraries of antigens and other peptides that bind to antibodies or receptors. In collaboration with R. Perham at the University of Cambridge, we are determining the three-dimensional structures of both designed and selected peptides. This is significant not only for analysis of these particular sequences, but also because short linear peptides are refractory to conventional methods of structure determination since they do not crystallize and tend to be highly flexible in solution. The folding of the peptides is enhanced by their interactions with the coat protein and the phage particles provide an ideal platform for the immobilization and orientation of the sequences for solid-state NMR studies. The sequences currently under investigation include the principal neutralizing epitope of HIV, GPGRAF, the main epitope of malaria, (NANP)n, and several others. The initial spectra are promising that the structural characterization can be carried out on the phage particles.